1. Field of the Invention
The present invention relates to a method and apparatus for monitoring fluid flow in a pipe or at an exit of a pipe, including sprinkler heads and leaks or breaks in the pipe.
2. Brief Description of the Prior Art
In an automatic fire sprinkler system in a commercial building, the water system servicing the sprinkler system is separate from the water system otherwise servicing the building. The presence of water flow in the sprinkler system is an alarm condition indicating that one or more of the sprinkler heads has fired. For the purpose of sounding an alarm, it is not necessary to determine how much flow is occurring, the presence of any detectable flow indicates a problem.
Typically flow detectors in an automatic fire sprinkler system are installed in the main water pipe as it enters the building. In simplest form, the flow detector comprises a flow switch including a large paddle inserted into the pipe. The slightest water flow in the pipe turns the paddle causing a switch to contact activating an alarm control circuit. There are also electronic flow detectors which can be inserted into the pipes for detecting flow. In the case of both mechanical and electronic flow detectors, one or more foreign elements is necessarily interposed in the path of the fluid whose flow is to be monitored. This has the disadvantage of distorting the flow one wishes to monitor; and the further disadvantage of necessitating the opening up of the pipe section to be monitored, prior to the monitoring operation, and either inserting the necessary functional elements or an additional pipe section, containing these elements, into the pipe system, which must then be resealed. Such an arrangement is costly and inflexible for detecting flow on a complex pipe system. Neither the mechanical nor the electronic flow detectors presently on the market provide any information regarding which sprinkler head has fired or how many sprinkler heads have fired which information is invaluable to the system operator or emergency personnel responding to the alarm.
There are other situations where the presence or absence of flow needs to be monitored. For example, the absence of flow through a spray nozzle may be significant to a farmer or a groundskeeper. If one or more of the nozzles fails to operate or operates unevenly, a part of the ground will not receive its proper dose of the liquid being spayed. Supervisory devices for detecting the presence or absence of flow through pipes in industrial processes are also needed. While it is possible to place a microphone or other acoustic sensor on the pipe or sprinkler to be monitored, in the systems known and used in the prior art, the information must be passed through a hard wired electrical system or radio transmitted to a central control panel.
There are electroacoustic fluid flow meters for determining the amount of fluid flowing through a pipe using contrapropagating transmission, reflection or Doppler methods. In contrapropagating transmission a pair of acoustic transducers are spaced a short distance apart on the pipe. By measuring the difference in time it takes an acoustic signal to pass between upstream and downstream transducers, it is possible to determine the rate at which the fluid is flowing through the pipe. For the purpose of the present invention, however, a flow detector, not a flow meter is required.